Space-time Block Coded Orthogonal Frequency Division Multiplexing Research Articles

Blind High-Order Modulation Recognition for Beyond 5G OSTBC-OFDM Systems via Projected Constellation Vector Learning Network

The blind modulation recognition (BMR) of high-order modulation types is a pressing task and needs to be raised in the calendar for the Beyond 5G (B5G) OSTBC-OFDM (Orthogonal Space-Time Block Coded-Orthogonal Frequency Division Multiplexing) system. In this letter, a BMR algorithm based on a project constellation vector which employs a temporal convolutional network (PCV-TCNet) is proposed to recognize 13 modulation formats, such as high-order 1024QAM and 2048QAM. Without any prior information, a zero-forcing blind equalization algorithm is leveraged to reconstruct the impaired signal. Furthermore, the learning content of PCV-TCNet is PCV features, which are transformed by the constellation diagram of the reconstructed signal. In addition, PCV-TCNet utilizes causal and dilated convolutions to accelerate the BMR process. The simulation results verify the proposed PCV-TCNet for recognizing the high-order modulation types in the B5G OSTBC-OFDM system and demonstrate its preferable recognition performance with the lowest complexity to existing methods.

A Novel LMMSE-EM Channel Estimator for High Mobility STBC-OFDM System

In time-selective fading channel, the Alamouti orthogonality principle is lost due to the variation of channel from symbol-to-symbol in space–time block-coded orthogonal frequency division multiplexing (STBC-OFDM) system and causes co-channel interference (CCI) effects. To combat the CCI effects, various signal detection schemes have been proposed earlier by assuming that a priori channel state information (CSI) is known to the receiver. However, in practice, the CSI is unknown and therefore accurate estimation of channel is required for efficient signal detection. In this paper, by exploiting circulant properties of the channel frequency response (CFR) autocorrelation matrix [Formula: see text], we propose an efficient low complexity linear-minimum-mean-square-error (LMMSE) estimator. This estimator applies an expectation–maximization (EM) iterative process to reduce the computational complexity significantly. Finally, we compare the proposed LMMSE-EM estimator with conventional least square (LS) and LMMSE estimator in terms of performance and computational complexity. The simulation results show that the proposed LMMSE-EM estimator achieves exactly the same performance as the optimal LMMSE estimator with much lower computational complexity.

Fast blind channel estimation for space–time block coded MIMO–OFDM systems

Fast blind subspace channel estimation using circular property of the channel matrix is investigated for space–time block coded (STBC) multiple-input multiple-output orthogonal frequency division multiplexing (MIMO–OFDM) systems in this paper. The noise subspace computed from the correlation matrix of received signals requires a large number of symbols to converge in the subspace channel estimation. Using the circular property of the channel matrix, we propose both the cyclic repetition method (CRM) and the forward–backward method (FBM) to generate N times of equivalent signals for each STBC–OFDM symbol, respectively, where N is the size of FFT operation. With these equivalent symbols, the proposed CRM, FBM and CRM–FBM (CFBM) channel estimations can perform very well within a few OFDM symbols. The CRM, FBM and CFBM schemes are applicable to the CP-OFDM, ZP-OFDM and VC-OFDM systems, respectively. The identifiability of the subspace channel estimation is investigated that the channel matrix is determined up to two ambiguity matrices. Computer simulations demonstrate that the CRM-based, FBM-based and CFBM-based channel estimations have better performances than the conventional ones.

Iterative Channel Estimation for Higher Order Modulated STBC-OFDM Systems with Reduced Complexity

In this paper, a frequency domain Expectation-Maximization (EM)-based channel estimation algorithm for Space Time Block Coded-Orthogonal Frequency Division Multiplexing (STBC-OFDM) systems is investigated to support higher data rate applications in wireless communications. The computational complexity of the frequency domain EM-based channel estimation is increased when higher order constellations are used because of the ascending size of the search set space. Thus, a search set reduction algorithm is proposed to decrease the complexity without sacrificing the system performance. The performance results of the proposed algorithm is obtained in terms of Bit Error Rate (BER) and Mean Square Error (MSE) for 16QAM and 64QAM modulation schemes.

A Maximum Likelihood (ML) based OSTBC-OFDM System over Multipath Fading Channels

This paper proposes a space-time block-coded orthogonal frequency-division multiplexing (STBC-OFDM) scheme for frequency-selective fading channels which does not require channel knowledge either at the transmitter or at the receiver. This paper proposed a generalized maximum likelihood estimation decoding algorithm. Due to the orthogonality nature of STBC, the rule for decoding was reduced to a single step. The performance investigation of the proposed system was done over Rayleigh fading channel and also over the Rician fading channel. Simulation results reveal the performance of proposed STBC communication system is near optimum.

Blind and semi-blind ML detection for space-time block-coded OFDM wireless systems

This paper investigates the joint maximum likelihood (ML) data detection and channel estimation problem for Alamouti space-time block-coded (STBC) orthogonal frequency-division multiplexing (OFDM) wireless systems. The joint ML estimation and data detection is generally considered a hard combinatorial optimization problem. We propose an efficient low-complexity algorithm based on branch-estimate-bound strategy that renders exact joint ML solution. However, the computational complexity of blind algorithm becomes critical at low signal-to-noise ratio (SNR) as the number of OFDM carriers and constellation size are increased especially in multiple-antenna systems. To overcome this problem, a semi-blind algorithm based on a new framework for reducing the complexity is proposed by relying on subcarrier reordering and decoding the carriers with different levels of confidence using a suitable reliability criterion. In addition, it is shown that by utilizing the inherent structure of Alamouti coding, the estimation performance improvement or the complexity reduction can be achieved. The proposed algorithms can reliably track the wireless Rayleigh fading channel without requiring any channel statistics. Simulation results presented against the perfect coherent detection demonstrate the effectiveness of blind and semi-blind algorithms over frequency-selective channels with different fading characteristics.

Joint Estimation of Transmitter and Receiver IQ Imbalance With ML Detection for Alamouti OFDM Systems

The application of multiple transmit antennas in orthogonal frequency-division multiplexing (OFDM) systems provides better spectral efficiency with high performance gain. However, these systems are very sensitive to channel estimation errors and analog front-end impairments, such as in-phase/quadrature-phase (IQ) imbalance. To ensure a reliable transmission, the channel impulse response (CIR) and IQ imbalance have to be accurately estimated. Unlike previous work, we show that the unwanted IQ imbalance can be exploited to achieve a diversity gain. This paper develops a maximum-likelihood (ML) detector by exploiting the diversity gain resulting from the IQ imbalance for Alamouti space-time block code OFDM systems. Moreover, we propose a novel iterative algorithm to jointly estimate the CIR and IQ imbalance occurring at both the transmitter and the receiver. We initially employ a pilot sequence for estimation and detection. Then, we exploit the soft information provided by the detector via an expectation-maximization (EM) algorithm to improve the estimation efficiency iteratively. To reduce the computational complexity of the estimation process, a suboptimal algorithm is also developed. Simulation results indicate that the bit-error-rate (BER) performance of the proposed detector in conjunction with the proposed estimation algorithms is very close to the BER of the perfectly known parameters case with a diversity gain resulting from the IQ imbalance.

Characterisation of impulse noise effects on space-time block-coded orthogonal frequency division multiplexing (OFDM) signal reception

This correspondence presents the characterisation of impulse noise effects on the space-time block-coded orthogonal-frequency-division-multiplexing (STBC-OFDM) symbol reception, in which the conventional OFDM system is combined with the antenna-diversity/spatial-diversity in order to achieve the high data transmission rates. The weak impulse noise may be combated by the longer OFDM symbol duration, in which the total energy of noise spreads among the simultaneously transmitted OFDM sub-carriers irrespective of the impulse noise energy distribution. Specifically, the focus of the presented work is on “noise bucket” effect, in which the STBC-OFDM system is considered to be working in the impulsive environment. It is demonstrated by simulation results that for the occurrence of a significant number of impulses per symbol duration, the noise distribution at the input of the receiver’s final decision device is approximately Gaussian. Therefore for simulation purpose, the impulsive environment may be generated by the mere incorporation of equivalent Gaussian noise. Besides, some simulation results are presented using 16-QAM / STBC-OFDM system to give some insight into the symbol error rate variations with respect to the different number of sub-carriers and characteristics of impulsive environment. Key words: Impulse noise, space-time block-coded (STBC), orthogonal-frequency-division-multiplexing, Gaussian distribution, i nverse discrete Fourier transform (IDFT), M-ary QAM.

Covariance precoding schemes for MIMO OFDM over transmit‐antenna and path‐correlated channels

AbstractThis paper considers covariance‐feedback based linear precoding (LP) and nonlinear Tomlinson–Harashima precoding (THP) for multiple‐input multiple‐output (MIMO) orthogonal frequency‐division multiplexing (OFDM) systems. Orthogonal space–time block coded (OSTBC)‡ OFDM and spatially‐multiplexed (SM)§ OFDM are analysed. The main objective is to design precoders to mitigate the impact of transmit‐antenna and path correlations. The impact of path correlations on the pairwise error probability (PEP) of MIMO OFDM is also analysed. Closed‐form, waterfilling‐based covariance precoders are derived to minimize the worst case PEP in OSTBC OFDM. An adaptive transmission strategy is also developed for switching between precoded SM OFDM and precoded OSTBC OFDM. The switching criterion is the minimum Euclidean distance of the received codebook. The switching decision sent to the transmitter requires one feedback bit per subcarrier. The proposed precoders considerably reduce the error rate in antenna and path‐correlated channels; nonlinear precoders perform better than linear precoders. We show that the adaptive strategy can achieve full diversity gain, and it outperforms either SM or OSTBC applied individually in terms of the bit error rate (BER). Copyright © 2010 John Wiley & Sons, Ltd.

Interference mitigation for asynchronous cooperative STBC-OFDM systems

This paper addresses the problem of interference mitigation in cooperative Space Time Block Coded Orthogonal Frequency Division Multiplexing (STBC-OFDM) systems in the presence of asynchronism. This scheme first preprocesses the received ST codewords to convert the equivalent fading matrix into a suboptimal ordering upper triangular form based on low complexity permutation QR decomposition, and then suppresses the InterCarrier Interference (ICI) and InterSymbol Interference (ISI) by exploiting Successive Interference Cancellation (SIC) technique. Simulation results show that the performance of the proposed algorithm slightly outmatches or asymptotically approaches to that of the existing Minimum Mean Square Error (MMSE) detector depending on the magnitude of the Carrier Frequency Offsets (CFOs) but with less complexity.

A Robust Channel Estimator for High-Mobility STBC-OFDM Systems

In this paper, a robust channel estimator for high- mobility space-time block code-orthogonal frequency division multiplexing (STBC-OFDM) systems is proposed and applied in IEEE 802.16e systems. A high-performance two-stage channel estimation method is adopted. The proposed architecture reduces computational complexity effectively and improves 85.2% of the hardware implementation. The performances of the proposed design have been demonstrated through the simulation of an STBC-OFDM system with two transmit antennas and one receive antenna. At the vehicle speed of 120 and 240 km/hr for quadrature phase shift keying (QPSK) modulation, the proposed design can achieve the bit-error rate (BER) of about 10-4 and 10-3 without using channel coding. Moreover, it has significant performance improvement as compared with interpolation-based channel estimation methods. The proposed channel estimator implemented in 90 nm CMOS technology can support up to 29.03 Mbps (uncoded) downlink data transmission. The design only requires 859.6 K gates and dissipates 43.71 mW at 83.3 MHz operating frequency with 1 V power supply.

Adaptive Subcarrier and Power Allocation with Fairness for Multi-user Space-Time Block-Coded OFDM System

This paper investigates the subcarrier and power allocation problems of multi-user space-time block coded OFDM based cellular systems. Based on the tradeoff between the number of assigned subcarriers and the amount of allocated power for users, a less complexity algorithm that separates subcarrier allocation and power allocation is proposed. Simulation results show that the proposed resource allocation algorithm can improve the capacity significantly compared with static FDMA fixed allocation algorithm and the MIMO-OFDMA scheme, and the more important thing is that it can make the capacity be distributed more fairly, very close to the ideal rate constraints, among users than the scheme which maximizes the system capacity only.

A Recursive ICI Cancellation Technique for Cooperative STBC-OFDM Systems with Carrier Frequency Offsets

In this letter, a recursive ICI cancellation technique for cooperative space-time block coded orthogonal frequency division multiplexing (STBC-OFDM) systems is proposed to mitigate the intercarrier interference (ICI) caused by multiple carrier frequency offsets (CFOs) in cooperative transmission. The proposed technique is shown to mitigate the noise enhancement effect on the STBC-OFDM signals caused by multiple CFOs, and to be effective in reducing ICI especially when the system has a large FFT size and multiple CFOs.

Bandwidth-efficient OFDM transmission with iterative cyclic prefix reconstruction

For orthogonal frequency division multiplexing (OFDM), cyclic prefix (CP) should be longer than the length of channel impulse response, resulting in a loss of bandwidth efficiency. In this paper, we describe a new technique to restore the cyclicity of the received signal when the CP is not sufficient for OFDM systems. The proposed technique efficiently restores the cyclicity of the current received symbol by adding the weighted next received symbol to the current received symbol. Iterative CP reconstruction (CPR) procedure, based on the residual intersymbol interference cancellation (RISIC) algorithm, is analyzed and compared to the RISIC. In addition, we apply the CPR method to Alamouti space-time block coded (STBC) OFDM system. It is shown that in the STBC OFDM, tail cancellation as well as cyclic reconstruction of the CPR procedure should be repeated. The computational complexities of the RISIC, the proposed CPR, the RISIC with STBC, and the proposed CPR with STBC are analyzed and their performances are evaluated in multipath fading environments. We also propose an iterative channel estimation (CE) method for OFDM with insufficient CP. Further, we discuss the CE method for the STBC OFDM system with the CPR. It is shown that the CPR technique with the proposed CE method minimizes the loss of bandwidth efficiency due to the use of CP, without sacrificing the diversity gain of the STBC OFDM system.

Maximum-Likelihood Detection of Orthogonal Space-Time Block Coded OFDM in Unknown Block Fading Channels

For orthogonal space-time block coded orthogonal frequency division multiplexing (OSTBC-OFDM) systems, many of the existing blind detection and channel estimation methods rely on the assumption that the channel is static for many OSTBC-OFDM blocks. This paper considers the blind (semiblind) maximum-likelihood (ML) detection problem of OSTBC-OFDM with a single OSTBC-OFDM block only. The merit of such an investigation is the ability to accommodate channels with shorter coherence time. We examine both the implementation and identifiability issues, with a focus on BPSK or QPSK constellations. In the implementation, we propose reduced-complexity detection schemes using subchannel grouping. In the identifiability analysis, we show that the proposed schemes can ensure a probability one identifiability condition using very few number of pilots. For example, the proposed semiblind detection scheme only requires a single pilot code for unique data identification; while the conventional pilot-based channel estimation method requires L pilots where L denotes the channel length. Our simulation results demonstrate that the proposed schemes can provide performance close to that of their nonblind counterparts.

A Robust STBC-Based Transmit Diversity Scheme for OFDM Systems Over Spatially Transmit Correlated Fading Channels

In this paper, we propose a robust space-time block coded (STBC)-based transmit diversity scheme with low decoding complexity against spatially transmit-correlated fading channels compared with the conventional STBC orthogonal frequency-division multiplexing (STBC-OFDM) schemes. The proposed scheme is comprised of Alamouti code for spatial diversity and a simple mapping process with subcarrier selection for frequency diversity. Proceeding from a detailed analysis of the rank and determinant of the channel correlation matrix, we present a proper subcarrier selection scheme satisfying the conditions for robustness against spatial transmit correlation. Furthermore, when the receiver employs a low-complexity decoder such as a zero-forcing decoder, the proposed scheme shows improved performance compared with the existing space-frequency coded OFDM schemes

Transmitter Precoding for ICI Reduction in Closed-Loop MIMO OFDM Systems

The mitigation of intercarrier interference (ICI) in closed-loop single-input-single-output (SISO) and multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) is considered. The authors show that the ICI coefficient matrix is approximately unitary and exploit this property to design a nonlinear Tomlinson-Harashima precoder for the reduction of ICI in closed-loop SISO OFDM and orthogonal space-time block-coded (OSTBC) MIMO OFDM. With the proposed design, the transmitter does not need to know the frequency offsets, and hence, their impact on the bit error rate (BER) is significantly reduced. Moreover, for spatially correlated MIMO channels, the precoder and OSTBC OFDM perform with a negligible BER-performance loss

Efficient ISI cancellation for STBC OFDM systems using successive interference cancellation

In this letter, we propose an efficient detection scheme for space-time block coded (STBC) orthogonal frequency-division multiplexing (OFDM) with insufficient cyclic prefix (CP). The proposed scheme employs successive interference cancellation (SIC) and cyclic prefix reconstruction (CPR) concepts. Simulation results present that the proposed scheme outperforms the conventional scheme for STBC OFDM systems.

Combined MMSE-SIC Multiuser Detection for STBC-OFDM Systems

In this letter, we propose a combined scheme of minimum mean square error (MMSE) detection and successive interference cancellation (SIC) for multiuser space-time block coded orthogonal frequency division multiplexing (STBC-OFDM) systems. With the same complexity order, the proposed scheme provides significant bit error rate (BER) performance improvement over the linear MMSE multiuser detector.

Combined ML and MMSE Multiuser Detection for STBC-OFDM Systems

Performance of the minimum mean square error (MMSE) detection is far below that of the maximum likelihood (ML) detection in a multiuser environment and decreases significantly as the number of co-channel users increases. In this paper, we propose a combined MMSE and ML multiuser detection scheme for space-time block coded (STBC) orthogonal frequency division multiplexing (STBC-OFDM) which has improved performance but with low complexity. In particular, we propose a reduced complexity ML post-detection (ML-PDP) scheme which can correct erroneously estimated bits from the outputs of MMSE multiuser detection. The proposed ML-PDP scheme performs sequential search to detect a predefined number of bits with higher probability of error and then uses ML detection to correct them. Upon controlling the number of corrected bits it is possible to balance the system performance with complexity associated with the ML-PDP. We show that significant improvement can be achieved at the cost of only small additional complexity compared with the MMSE multiuser detection.